1. Field of the Invention
The present invention relates to a rotor for a fan or compressor stage of a turboshaft engine, of the type comprising a rotor disc, an array of radial blades mounted in axially extending sockets formed in the periphery of the disc, a series of spacer blocks disposed between the blades so as to maintain the inter-blade spacing, means for attaching the spacer blocks to the disc, and means for axially retaining the blades in their respective sockets, each of said spacer blocks having an outer wall which is spaced from the periphery of said disc and which, together with the outer walls of the other spacer blocks, defines the inner boundary of the fluid flow path from upstream to downstream through the rotor.
This type of rotor is particularly used in stages of large diameter because it is imperative, on the one hand, to limit the diameter of the disc carrying the blades on account of the considerable centrifugal force exerted at high rotational speeds of the turboshaft engine and, on the other hand, to increase the inner diameter of the path of fluid flowing from upstream to downstream through the stage so as to have a generally uniform speed of flow of the fluid throughout the whole cross section of the path.
In the case of blades of small size, it is common practice to use blades with platforms. But when the blades are of large size, this technique is undesirable because it involves a substantial increase in the weight of the blade roots.
2. Summary of the Prior Art
British Patent No. 2 006 883 in particular discloses a rotor for a stage of a turboshaft engine of the type mentioned above. The spacer block described in this patent comprises, at the rear, a hook which is directed upwards and engages with a matching groove provided in a first retaining ring attached by a bayonet fixing to the rear face of the disc and, at the front, a rib which extends towards the axis of the disc and co-operates with the front face of the disc to prevent axial movement of the spacer block towards the rear. A second retaining ring is fixed by bolts on the front face of the disc to connect the front end of the spacer block to the disc.
With this mode of construction and fixing, it is necessary for the spacer block to have an inner wall which only partially bears against the periphery of the disc in such a way as to enable the rear hook to be engaged in the corresponding groove of the first retaining ring by tilting the spacer block on the periphery of the disc. This results in a complex configuration for the spacer block and an increase in weight. In addition, the bayonet fixing arrangement serving to fasten the first retaining ring to the rear face of the disc requires a difficult machining operation on the disc and on the ring.